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Unformatted text preview: omenet2run/tcpip/tcp-ip-illustrated/introduc.htm (10 of 20) [12/09/2001 14.46.31] Chapter 1. Introduction Figure 1.8 The demultiplexing of a received Ethernet frame.
Positioning the protocol boxes labeled "ICMP" and "IGMP" is always a challenge. In Figure 1.4 we showed
them at the same layer as IP, because they really are adjuncts to IP. But here we show them above IP, to reiterate
that ICMP messages and IGMP messages are encapsulated in IP datagrams.
We have a similar problem with the boxes "ARP" and "RARP." Here we show them above the Ethernet device
driver because they both have their own Ethernet frame types, like IP datagrams. But in Figure 2.4 we'll show
ARP as part of the Ethernet device driver, beneath IP, because that's where it logically fits.
Realize that these pictures of layered protocol boxes are not perfect. When we describe TCP in detail we'll see that it really demultiplexes incoming segments using
the destination port number, the source IP address, and the source port number. 1.8 Client-Server Model
Most networking applications are written assuming one side is the client and the other the server.
The purpose of the application is for the server to provide some defined service for clients.
We can categorize servers into two classes: iterative or concurrent. An iterative server iterates
through the following steps.
I1. Wait for a client request to arrive.
I2. Process the client request. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/introduc.htm (11 of 20) [12/09/2001 14.46.31] Chapter 1. Introduction I3. Send the response back to the client that sent the request.
I4. Go back to step I1.
The problem with an iterative server is when step I2 takes a while. During this time no other
clients are serviced. A concurrent server, on the other hand, performs the following steps.
Cl. Wait for a client request to arrive.
C2. Start a new server to handle this client's request. This may involve creating a new pro...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12